The invention relates generally to drills and, more specifically, to multi-bit drill that provides successes sharp drill tips throughout the use.
Drills and drill bits are common to the art. Generally, drills are used to create holes in solid objects, commonly wood or metal. In metalworking, drills are used to make initial holes ranging from 0 to 5/16 inch. Diameters above 5/16 inch usually are made in a second operation, enlarging the predrilled pilot hole. For example, if the craftsman wants to drill a 9/16 inch hole, he would use a 5/16 inch drill for the first operation and then drill the 9/16 inch hole. Thus, the 9/16 inch drill would cut 1/8 inch per each cutting edge.
A typical prior art twist drill, shown as 10 in FIG. 1, normally has a fluted land 11 comprising tip 12 and only two cutting edges 14 and 16 with corresponding two flutes 17 and 18 to accommodate the chips. If there is need for a more accurate holes, two-fluted drills do not do a very precise job. To make a more precise hole, core drills are used. A core drill typically includes three or more flutes, and provide better accuracy and a better finish. FIG. 1 illustrates a standard, prior art, three-fluted core drill. FIG. 6 illustrates a prior art, three-fluted twist drill having a coating of tin.
Prior art drills, both two-fluted drills and three or four-fluted core drills, must remain sharp to perform well. Sharpening an ordinary two-fluted drill up to 1/2 inch, for example, is possible on a bench grinder, but requires the skill of an experienced craftsman to do a good job. Many drill users, for example home users or "do-it yourselfers" who do not have the tools or the skill to sharpen drills. Since these users cannot restore the cutting edge of the drill, the drill life is short. Thus, the user employs low cost drills which are discarded when they become dull. This makes economic sense, however, the low cost drills also lack in performance.
Further, most high quality drills have a surface treatment of nitride case, black oxide or tin. A premium tin coated drill may have 400% greater performance than an untreated drill. However, after a first grind to sharpen the drill, the surface treatment at the cutting edge is removed.
Also, the drill manufacturing industry is employing more exotic materials, for example carbide and ceramic, for making drills which are hard to machine and sharpen.
It would be advantageous, therefore, to provide a drill that creates a precise finished hole and maintains a sharpened, preferably coated, cutting edge.